Thermostat controlled systems for heating furnaces and/or air cooling systems (hereinafter collectively referred to as "furnaces") of the type employed in residences and many commercial and industrial buildings often include means for manually entering a desired temperature set point, means for measuring the actual temperature within the building, and means for switching the furnace on or off as a function of the difference between the set point temperature and actual temperature.
The availability of inexpensive integrated circuits incorporating large numbers of digital devices on a single semiconductor chip has lead to the development of programmable electronic thermostats including means for storing a schedule of desired temperatures at specified times within a respective period such as a day or a week. For example, U.S. Pat. Nos. 4,206,872 and 4,314,665, disclose a thermostat for generating control signals for a furnace employing a digital memory for storing a desired temperature-time program for the thermostat for a repetitive period.
While electronic programmable thermostats enjoy both cost and reliability advantages over conventional mechanical thermostats, they are often limited in their operation and may be difficult or inconvenient for the average homeowner to program and operate.
In particular, the limited data entry means and limited displays often make it difficult for homeowners unfamiliar with simple computer device programming to succesfully program the device or take advantage of all of the features offered by the device.
It is therefore an object of the present invention to provide a programmable thermostat including a display having simple, clear, graphic indications of the current mode and operable parameters, and simple, easy-to-understand program entry means to ensure efficient "user friendly" programming and operation by a typical homeowner.
It is another object of the present invention to provide a programmable thermostat including means for entering a desired temperature for the heating unit and a desired temperature for the cooling unit for each of the times in the time-temperature schedule.
It is another object of the invention to provide display means for displaying the two temperatures associated with the particular time-temperature point in a schedule as a range of temperatures, bounded at either end by the desired heating and cooling temperatures respectively.
It is yet another object of the present invention to provide an electronic programmable thermostat including means for entering an entire time-temperature schedule at one time.